The field of the invention relates generally to encapsulation of relatively fragile devices such as electronic components and, more particularly, to a system, process, and a product made by the generic process of rapid injection molding. The system has no slurry valves, a novel mix head with improved slurry handling, a high intensity mixer, and novel chemical handling and dispensing mechanisms.
The system described herein is designed to meter, mix, and initiate chemical and chemical slurry streams for reaction injection molding of small parts. While encapsulation of electronics circuits and discrete components is the primary intended use of this technology, it could also be used in other applications, such as the making of small parts to replace transfer compression moldings made of other filled or fiber reinforced thermosetting materials such as epoxy, phenolics, and alkyds.
Conventional electronic component encapsulation methods use epoxy transfer molding that require relatively slow mold cycle times of 60 to 120 seconds followed by relatively long oven curing times of 2 to 4 hours. These long time intervals are dictated by the rate of polymerization of the premixed materials, the rate of which is set to a low value to provide a reasonable shelf life, and to allow for mixing time by the compounder and handling time by the end user. The need for the long oven curing times is to ensure complete polymerization. Damage to fragile electronic interconnections sometimes results from conventional encapsulation methods when the material viscosity becomes excessive due to improper storage conditions. It is also necessary to remove residual corrosive materials from the epoxy, which greatly increases the cost of its manufacture. Moisture absorption is another potential problem with epoxy materials used in conventional electronic component encapsulation methods. These methods also require a relatively high mold temperature which can lead to thermal stresses in the encapsulating package.
For the foregoing reasons, there is a need, therefore for an encapsulating system that provides a short mold cycle time with no required oven curing, provides mixing of reactive materials just prior to injecting the materials into a mold, provides chemical material handling capability that requires no special storage, handling, or mixing by trained personnel, eliminates damage to fragile electronic interconnections caused by excessive material viscosity, eliminates the need for removing corrosive byproducts in the chemical components, reduces moisture absorption in the encapsulated product, and reduces thermal stresses in the encapsulated product.